Multibeam Sonar Theory of Operation
Multibeam Sonar Theory of Operation
Multibeam Sonar Theory of Operation
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Sidescan <strong>Sonar</strong> <strong>Multibeam</strong> <strong>Sonar</strong> <strong>Theory</strong> <strong>of</strong> <strong>Operation</strong><br />
Mapping Sidescan Values for 2000 Pixel Resolution<br />
The final stage <strong>of</strong> sidescan data processing is mapping the detected echoes to build an image <strong>of</strong><br />
the sea floor. In detecting the echoes <strong>of</strong> a specific ping, the SEA BEAM 2100 monitors the<br />
particular set <strong>of</strong> sequential time slices that generally range between when the first (nearest) and<br />
last (farthest) bottom echoes are expected. This range is controlled by the SEA BEAM 2100<br />
operator through the Start and Stop Gates settings (see Chapter 9 <strong>of</strong> the SEA BEAM 2100<br />
Operator’s Manual for information about the theory and operation <strong>of</strong> the Start and Stop Gates<br />
settings).<br />
Recall that the sidescan process collects the echoes from a swath <strong>of</strong> the sea floor that is oriented<br />
perpendicular to the path <strong>of</strong> a survey vessel. For each bottom swath, the SEA BEAM 2100<br />
sidescan data is mapped into an array <strong>of</strong> 2000 pixel locations. This array contains the amplitudes<br />
<strong>of</strong> echoes from the sea floor. The physical size represented by these 2000 pixels is determined by<br />
the value <strong>of</strong> sidescan pixel size, which is set by the SEA BEAM 2100 operator (see Chapter 10<br />
<strong>of</strong> the SEA BEAM 2100 Operator’s Manual for information on setting sidescan pixel size). For<br />
instance, if the sidescan pixel size is set to 2 meters per pixel, the 2000-pixel sidescan swath is<br />
4000 meters wide. In all cases the mapped swath is centered directly below the path <strong>of</strong> the survey<br />
vessel.<br />
The echoes from all relevant time slices are added to the sidescan swath array. The echo angles<br />
are converted to physical locations on the bottom based on sound velocity. These are then mapped<br />
into the pixels in the sidescan swath array (see Figure Chapter 5 - -16). Amplitudes <strong>of</strong> echoes that<br />
fall within the physical limits <strong>of</strong> the 2000 pixel swath are retained; all others are discarded. At the<br />
conclusion <strong>of</strong> the process, some pixels will have no echoes recorded in them, some will have one,<br />
and others will have many. Pixels that have one echo are assigned the amplitude <strong>of</strong> that echo. If a<br />
pixel has more than one echo, the average <strong>of</strong> the amplitudes is used. Pixels with no reported<br />
echoes are assigned a value interpolated from neighboring pixels.<br />
Page 5-14 Copyright © 2000 L-3 Communications SeaBeam Instruments<br />
No portion <strong>of</strong> this document may be reproduced without the expressed written permission <strong>of</strong> L-3 Communications SeaBeam Instruments